1. Field of the Invention
The present invention relates to a headbox for a paper machine that includes a turbulence insert, a distributing pipe extending across a machine width for feeding a slurry flow into the turbulence insert, a nozzle having an outlet gap, and a plurality of feed lines for supplying a control flow. The plurality of feed lines, in a connecting area of the distributing pipe, may be provided in a vicinity of the turbulence insert at an angle .alpha., e.g., between approximately 5.degree. and 170.degree., relative to a direction of the slurry flow toward the turbulence insert. In this manner, the consistency of the slurry flow can be adjusted to a desired value at an input area of the turbulence insert by control flows injected via the plurality of feed lines, while maintaining a constant volumetric slurry flow in the input area.
The present invention also relates to a process for controlling the consistency and fiber orientation cross-sectional profile in a headbox. The process may include feeding a slurry flow to the headbox across an overall machine width, controlling the consistency profile of the slurry flow via a plurality of control flows distributed across the machine width, while maintaining a volumetric flow of the slurry flow at a constant rate. The process may include injecting the control flows into the distributing pipe, at an angle .alpha., e.g., between approximately 5.degree. and 170.degree., to a direction of the slurry flow toward the turbulence insert. In this area, i.e., immediately before the turbulence insert, the slurry flow may substantially include only a flow component in the direction of the turbulence insert. Further, the process may include diverting the injected control flows in the distributing pipe at an angle less than approximately 180.degree. to have a flow direction parallel to the slurry flow.
2. Discussion of Background Information
Consistency-controlled headboxes for adjusting or controlling the consistency and fiber orientation cross-sectional profile are known in the prior art. These devices generally utilize two different concepts. A first concept, according to U.S. Pat. No. 5,196,091, shows a headbox provided with a pulp slurry via a distributing pipe extending across the entire machine width. The distributing pipe in this device cannot be sectioned. Connected to the distributing pipe is a machine-wide turbulence insert which has a plurality of evenly arranged columns and rows of turbulence pipes.
Between the evenly arranged turbulence pipes, feed lines are arranged parallel to the pipes for adding a diluting medium which can be water or diluted pulp slurry.
To control the consistency profile across the machine width, a corresponding amount of diluting medium is injected via the diluting medium feed lines, however, the amount depends on the value of the desired consistency in the turbulence section. In this case, the diluting or control flow emerging from the distributing pipe is directed opposite the slurry flow entering the turbulence pipe.
Thus, dilution occurs as the control flow is diverted 180.degree. by the slurry flow. While the slurry flow may be slow in the distributing pipe, the control flow is diverted to flow along the width of the machine together with the slurry flow. The diluted slurry flow is fed into an inlet side of a turbulence pipe of the turbulence insert. In this manner, the slurry flow is controlled while the volume flow is maintained at a constant level and not by the feed rate into the distribution pipe.
The disadvantage of headboxes according to the above-noted first concept is that, due to the very small diameters of the diluting pipes, the outlet speed of the diluting media or control flows within the distributing pipe is very high. This causes a relatively large transverse effect on the control flow, which allows for only a very rough setting of the consistency in individual sections of the headbox. Moreover, thin pipes of the type utilized in the prior art only allow the dosing of very small quantities. Thus, the range in which the consistency can be controlled, which is relative to the specified mean consistency of the slurry flow entering the distributing pipe, is very small.
A second concept of a consistency-controlling headbox is disclosed, e.g., in DE 40 19 593. According to DE 40 19 593, the slurry flow, which is fed by a common distributing pipe, is sectioned, i.e., subdivided across a width of the headbox into independent partial flows, i.e., so-called "sectional flows." This sectioning occurs, e.g., by subdividing the width of the headbox into sections via partition walls.
The setting of the consistency then occurs by feeding the control flow in the individual sections of control flow into a mixer. Connected to the mixer, a turbulence insert is coupled and associated with the individual sections. Further, in the concept in accordance to DE 40 19 593, the consistency of the corresponding sectional flows is set, e.g., while the volumetric flow of the sectional flow is maintained at a constant rate.
The system of DE 40 19 593 utilizes a sectioned headbox, which is known from DE 43 23 263. In this manner, the control flow is injected into the individual sections at angles between 5.degree. and 90.degree. in the direction of the main flow.
Further, a control method has been discussed, e.g., in DE 42 39 845, in which the consistency and fiber orientation profile can be controlled depending on the specifics of the sheet making process.
The disadvantage with headboxes constructed in accordance with the second concept is that the setting of a consistency and fiber orientation cross-sectional profile always preconditions that the slurry flow is divided into partial flows to be correspondingly controlled in the adjoining mixer for the individual sections.
This disadvantage results in high design expenditure. Further, due to the size of the device, the configuration commands high space expenditure.